Lithographic processes generally employ at least two steps to prepare a plate for use in a printing press, namely exposure of a plate coated with a photosensitive composition to a positive or negative light source to create a photoimage and a subsequent development step. Typically in a negative-acting system, the development step involves washing away material from the plate which was unexposed to the light source with the aid of a developer solution which may be highly alkaline, e.g. pH of 13, and based on an organic solvent. Alternatively, heating has sometimes been employed to effect development of the photoimage.
Both of the above-described development processes, though, suffer from the drawback of being relatively time-consuming and expensive in some instances. Furthermore, when volatile organic or strongly alkaline developer solutions are used, their disposal presents an environmental problem.
What have been needed in the industry, therefore, are photosensitive compositions which can be used in development processes which do not have the above-described drawbacks.
A variety of different materials have been used in photosensitive compositions in the past. Photosensitive compositions employing polymers with pendant acid sensitive moieties have been described in the art (Ito, H.; Ueda, M. Macromolecules 1988, 21, 1475-82). o-Nitrobenzyl substituted polyacrylates have been described in U.S. Pat. No. 3,849,137 (Nov. 19, 1974; Barzynski). t-Butyl substituted polyacrylates have also been reported (Ito, H.; Willson, C. G. in Proc. SPIE-Int. Soc. Opt. Eng. 1987, 771, 24; and U.S. Pat. No. 4,491,628 (Jan. 1, 1985; Ito). U.S. Pat. No. 4,963,463 (Koshiba et al.) claims a radiation sensitive resin composition comprising an alkali soluble resin, an o-quinone diazide, an aci sensitive esters of nitrobenzyl or cyanobenzyl alcohol.
End-capped polyphthaladehyde has been employed in imaging systems in combination with onium salts which were used as a source of photogenerated acid (Ito, H.; Willson, C. G. Polym. Eng. Sci. 1983, 23, 1013). Photoresists based on thermal polycarbonate degradation in the presence of photogenerated acid have also been described (Frechet, J. M. J.; Bouchard, F.; Houlihan, F. M.; Kryczka, B.; Eichler, E.; Clecak, N.; Willson, C. G. J. Imag. Sci. 1986, 30, 59). Both of these systems function by cleavage of the polymer backbone.
Canadian Patent No. 672,947 (Canadian Industries Ltd.) describes protective films comprising copolymers of tetrahydropyran-2-yl acrylates, and glycidyl esters of acrylates. These films are thermally processed, thereby effecting cleavage of the tetrahydropyran-2-yl groups, and subsequently causing cross-linking of the carboxylic acid and the epoxy residues.
Benzyl, benzhydryl, and triphenylmethyl acrylates have been imaged using high energy radiation (e.g., electron beam, x-ray, and ion beam) sources followed by development with aqueous alkaline solutions as described in Japanese published applications 59-075244 (Apr. 27, 1984; Hitachi, Ltd.), and 58-068743 (Apr. 23, 1983; Hitachi, Ltd.).
Dimethylbenzyl methacrylates have been employed in combination with iodonium salts as deep-UV photoresists (Ito, H. Polym. Mater. Sci. Eng. 1989, 60, 142).
.alpha.-Substituted benzyl methacrylate polymers have been photoimaged and developed with an alkaline developer (Ito, H.; Ueda, M.; Ebina, M. ACS Symp. Ser. 1989, 412, 57-73).
Japanese published applications 63-256492 (Oct. 24, 1988; Fuji Photo Film Co., Ltd.) and 63-317388 (Dec. 26, 1988; Fuji Photo Film Co., Ltd.) describe several direct-image lithographic plate formulations employing polymers having side-chain groups which, following an etching development step, cleave to form hydroxyl and carboxyl groups.
Japanese published patent applications 53-094691 (Oct. 24, 1989, Fuji Photo Film) and 53-100192 (Oct. 30, 1989, Fuji Photo Film) describe lithographic plates containing polymers with acid labile groups including some alkoxyalkyl esters. The plates also contain cross-linking agents which appear to cross-link with carboxylic acid residues as they are formed. These plates appear to act in a negative-tone and may involve a development step.
Japanese published application 62-299,313 (Jun. 1, 1989, Matsushita Electric Industrial) describes the use of polymers containing acid anhydride residues in combination with o-nitrobenzyl esters of carboxylic acids. These polymers are sensitive only to UV radiation.